Two-cycle engine with exhaust temperature-controlled ignition timing

ABSTRACT

A two-cycle internal combustion engine has an ignition timing that varies with engine speed. A plurality of ignition patterns (the relationship between ignition timing and engine speed) are used. The engine exhaust gas temperature is sensed and is used to determine the particular ignition pattern used at a particular time.

CROSS REFERENCE TO RELATED APPLICATION

[0001] This application is a continuation-in-part of Ser. No.09/452,657, filed Dec. 1, 1999, the disclosure of which is incorporatedherein by reference.

BACKGROUND OF THE INVENTION

[0002] The present invention is directed to a two-cycle internalcombustion engine and the operation of such an engine. Such engines areused, for example, to drive various vehicles such as snowmobiles,motorcycles, personal watercraft and others.

[0003] The operation of such engines is based on the ignition of acompressed fuel-air mixture within a cylinder, with the resultingexpansion of the ignited mixture driving a reciprocating piston locatedin the cylinder. The reciprocating movement of the piston then is usedto drive the vehicle powered by the engine.

[0004] It is desirable to vary the point during the reciprocation cycleof the piston at which the fuel-air mixture is ignited, i.e. a pointbetween “bottom dead center” and “top dead center”, to provide optimumoperation of the engine. Thus, as one example the optimum point ofignition during acceleration can differ from that for a normal runningoperation. Because the piston usually is driven by a rotating crankshaft, the ignition point often is expressed in terms of degrees ofadvancement with respect to top dead center, in other words the positionwith respect to degrees of rotation of the rotating crank shaft ahead ofthe top dead center position.

[0005] Typically, different engine operating speeds, which usually areexpressed in revolutions per minute, will be associated with differentengine conditions. For example, higher engine speeds often areassociated with acceleration. Thus, it has been considered that thepoint of ignition during the reciprocation cycle of the piston should bevaried, depending on the engine operating speed at the particular time,and engine ignition control systems can be programmed to vary theignition point depending on the engine speed.

[0006] Other factors can affect the optimum ignition timing. Forexample, an engine operating shortly after start-up may require adifferent relationship between ignition timing and engine speed(hereinafter “ignition pattern”) than an engine that has been operatingfrom some time. Consideration has been given in the past to a systemthat allows the user to switch between two different ignition patterns.This has not been completely satisfactory in optimizing engineperformance.

SUMMARY OF THE INVENTION

[0007] The present invention seeks to provide a two-cycle engine thatenjoys improved performance by selecting from a plurality ofrelationships between ignition timing and engine speed (ignitionpatterns) based on exhaust gas temperature. In one aspect of the presentinvention, individual ignition patterns cover ranges of exhaust gastemperature of about 50 C. The sensitivity of the control systemincreases as the temperature range decreases. In another aspect of thepresent invention the exhaust gas temperature is determined by use of asensor that is in contact with the exhaust gas, for example in anexhaust pipe. In a further aspect of the invention, a capacitordischarge ignition system is used to control the ignition timing of aspark plug. Yet another aspect of the invention provides for a defaultignition pattern when there is a malfunction of the temperature sensor.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008]FIG. 1 is a schematic illustration of an example of an engine inaccordance with the present invention.

[0009]FIGS. 2 and 3 are flow charts illustrating examples of the controlof the ignition timing.

[0010] FIGS. 4-8 are graphs illustrating examples of different ignitionpatterns that can be used in the present invention.

DETAILED DESCRIPTION

[0011] The present invention will be described with reference to theaccompanying drawings. It should be understood that the presentinvention is not limited to the specific embodiments of this descriptionand the drawings.

[0012] Referring to FIG. 1, a two cycle engine 10 includes a cylinder 12and piston 14 that moves reciprocally within the cylinder. The movementof the piston 14 may be controlled with a crank shaft 16. Fuel-airmixture introduced into the cylinder is compressed during the upwardmovement of the piston with in the cylinder and is ignited by anignition source 18, for example a spark plug. The expansion resultingfrom the resulting combustion drives the piston downward, therebyimparting rotation to the crank shaft, which in turn can be used todrive a vehicle on which the engine is mounted. Examples of vehiclesthat typically make use of such two cycle engines include snowmobiles,personal watercraft, motorcycles and the like, although the presentinvention is not limited thereto. In addition, the present inventioncould be applied to two cycle engines used in a stationary setting ifdesired. Exhaust gas resulting from the combustion of the fuel-airmixture is expelled from the cylinder, for example through an exhaustpipe 28. The present invention is not limited to any particular exhaustsystem, and various combinations of exhaust pipes and manifolds can beused with engines that have more than one cylinder.

[0013] Controller 20 is provided for controlling the ignition of theignition source 18. In one embodiment, the controller is a capacitordischarge ignition system, and activates a spark plug through coil 22.However, other ignition and control systems can be used as well, such aselectronic ignition systems. Generally, the ignition should take placewhile the piston is moving upwardly, i.e. during the compressionmovement by the piston. Typically the ignition takes place shortlybefore the piston reaches the end of the compression movement (the “topdead center” position). The ignition timing can be expressed withrespect to the rotation of the crank shaft, i.e. in terms of a certainnumber of degrees before the top dead center position.

[0014] Different effects of the combustion can be achieved by varyingthe ignition timing. Thus, depending on the desired affect, in somecases it is desirable to have an earlier or “advanced” ignition. Thecircumstances in which particular effects are desired can be correlatedto engine speed. Thus, at a particular engine speed a particularadvancing of the ignition timing will be used. In some ignition systems,the ignition timing is based only on engine speed (so-called2-dimensional ignition systems). In other ignition systems, timing isbased on engine speed and throttle position (so-called 3-dimensionalignition systems). Both are applicable to the present invention. In anycase, the various combinations of ignition timings and particular enginespeeds thus will form a particular ignition pattern.

[0015] Different engine operating conditions may result in differentignition patterns being desirable. That is, in one circumstance oneparticular ignition pattern may be the most useful, while anotherpattern might be better under different conditions. In accordance withthe present invention, the exhaust gas temperature is used to evaluateoperating conditions and thus determine which of two or more ignitionpatterns should be selected for engine operation. For this purpose, anexhaust gas temperature sensor 24 is provided. It is preferred that thesensor 24 be in direct contact with the exhaust gas for the purposes ofaccuracy and reduction in reaction time, for example by being positionedin the exhaust pipe 26. However, it is possible to sense the temperatureon the outside of part of the exhaust system or to sense the temperatureof water in a water jacket surrounding an exhaust pipe. In the case of asensor directly contacting exhaust gas in the exhaust pipe or other partof the exhaust system, the sensor should be able to withstand thatenvironment, and suitable measures should be taken to seal the exhaustsystem at the point where the sensor extends into the exhaust system. Anexample of a suitable sensor for use in directly contacting the exhaustgas is a thermistor. It is desirable that the sensor be positioned inthe exhaust system at a position sufficiently far from the engine toavoid sharp rises and falls (spikes) in temperature of short duration.However, if the sensor is too far from the engine the responsiveness ofthe system is adversely affected, i.e. there will be too much delay insensing increases and decreases in temperature. The exact position isdetermined based on the specific characteristics of the exhaust systeminvolved.

[0016] The sensor 24 provides information concerning the exhaust gastemperature to the controller 20. For example, in the case where athermistor is used as the sensor, the sensor sends an electrical signalwhose magnitude changes with changes in the exhaust gas temperature. Thecontroller then selects an ignition pattern based on the exhaust gastemperature information. The selected ignition pattern then is used tocontrol the ignition advance based on the engine operating speed. Inthis regard, a signal can be sent from the crank shaft to the controllerto indicate the engine speed and the relative position of the crankshaft so that the desired ignition timing can be provided.

[0017] The controller can process the temperature information asdesired. For example, in one embodiment the controller can take theaverage of several readings, e.g. 10, with the readings being taken bythe sensor every 2 milliseconds as one example. Other methods forhandling the sensor information can be used as well.

[0018] It is desirable to have a plurality of ignition patterns, each ofwhich covers a particular temperature range. As one example, fivepatterns could be provided, each of which covers a range of about 50 C.,for example from 250 C. and lower, 250-300 C., 300-350 C., 350-400 C.,400 C.+ respectively. Different numbers of patterns and differentcombinations of ranges can be used as desired for a particular practicalapplication, and it is possible to have the different patterns in asingle application cover larger and smaller temperature ranges as neededfor that particular engine.

[0019] A default ignition pattern can be provided for cases where thereis a failure in the temperature sensor. Sensor failure can bedetermined, for example, by the sensor reading temperatures outsideexpected parameters, e.g. reading above or below certain limits. Thus,as one example, a temperature reading higher than the upper sensor faillimit would be interpreted as a short in a thermistor sensor, while areading below the lower sensor fail limit would be interpreted as abreak in the wiring in a thermistor sensor. It also is possible to allowfor user selection of ignition patterns in the event of sensor failure.

[0020] It also is possible to use the sensed temperature readings tomodify a particular timing pattern that can be selected from a pluralityof patterns. For example, the user may be able to select a timingpattern from a plurality of timing patterns using a switch or the like,and the sensed temperatures readings can be used to modify the selectedpattern appropriately.

[0021] Further, in some cases the desired engine timing pattern maydepend on the type of fuel being used in the engine. In such cases, thesensed exhaust temperature may be indicative of the type of fuel and canbe used to set the ignition timing pattern accordingly. Thus, the sensedtemperature can compensate for the type of fuel used, or can be used toselect a timing pattern that would avoid damage to the engine if thefuel selected is not desirable for the engine.

[0022] The sensed exhaust temperature also may be useful in indicatingsome problem in engine performance, e.g. incorrect carburetion or fueldelivery. Again, in this case the sensed temperature can be used toselect a timing pattern that avoids damage to the engine.

[0023] An example illustrating the control of the ignition timing willbe discussed with respect to FIGS. 2-8. In this embodiment, a thermistortype sensor is used. FIG. 2 illustrates the control from the enginestart time. At the time the engine is started, the temperature sensor isreset. The controller then determines whether the temperatureinformation is lower than the upper sensor fail limit temperature, e.g.600 C. as one example in a case of an engine for a snowmobile. If not,the controller considers that the sensor is shorted out and switches toa “hold pattern”, which operates as a default pattern. Any of theavailable ignition patterns can be used for the default pattern, or theuser can be permitted to select one of the available patterns, or aspecial pattern can be used. If the temperature is below the uppersensor fail limit, the controller continues and determines whether theengine has been running for a sufficiently long period before the failcontrol is initiated (fail control delay time). Essentially, thispermits the engine to run for a period during which the exhaust gastemperature would be expected to exceed the lower sensor fail limittemperature. Until this period is passed, the controller checks onlywhether the sensor is reading a temperature below the upper sensor faillimit, and if not the “hold pattern” is invoked. The delay period willdepend on the lower temperature limit of the sensor, and in the case ofa sensor having a lower limit of about 200 C. the delay period generallywill be around 10-2500 seconds, with a delay of 120 seconds beingtypical.

[0024] Once the fail control delay time is passed, a further short delaytime can be invoked, e.g. on the order of five seconds. This permits theuse of a different default pattern during this period under certaincircumstances. If the sensor reading is above upper sensor fail limit,the “hold pattern” is invoked. If the sensor reading is below the lowersensor fail limit an “information pattern” can be invoked, which can bethe same as or different from the “hold pattern”. The informationpattern can be such that the pattern would warn the user of sensorfailure if a failure indicator light is not provided. An example of alower sensor fail limit is 225 C. for a thermistor sensor used in a twocycle snowmobile engine. If the sensor reading is between the upper andlower sensor fail limits, a “normal” pattern is selected. The furtherdelay period should be sufficient for the controller to check for sensorfailure, for example about 5 seconds or so.

[0025] Once the further delay has passed, and assuming the “holdpattern” has not been invoked, the sensory memory function is activated(if sensor output information is to be based on averaged values ofprevious readings) and normal control is invoked. Referring to FIG. 3,if the “information pattern” was invoked during the further delay, thispattern continues until the exhaust temperature is between the upper andlower sensor fail limits. If the “information pattern” was not invokedduring the further delay, i.e. one of the normal patterns was selected,the exhaust temperature is checked to determine whether it is betweenthe upper and lower sensor fail limits. If so, the selection of one ofthe normal patterns continues. If not, the “hold pattern” is invoked,after which the system can recheck itself to determine whether there hasbeen sensor failure (Start Memory Sensor).

[0026] The graphs of FIGS. 4-8 show amount of ignition advance (indegrees before top dead center) as the ordinate versus engine speed(rpm) as the abscissa for five different temperature ranges for a twocycle snowmobile engine. The Figures represent the ignition patterns for250 C. and lower, 250-300 C., 300-350 C., 350-400 C. and 400 C.+respectively.

[0027] A further example of data that can be used to generate curves ofthe type shown in FIGS. 4-8 is presented below. In these data, the“angle” represents the number of degrees before top dead center. RPMANGLE A. Exhaust Temperature 250 C. or less 8800  7.0 8600  7.0 8400 7.0 8200  8.0 8000 10.0 7750 12.5 7500 14.5 7250 16.0 7000 17.5 650020.0 6000 24.0 5000 24.0 4000 20.0 3000 10.0 2000 10.0 1000  8.0 0000 8.0 B. Exhaust Temperature 250-300 C. 8800 11.0 8600 10.0 8400  7.08200  8.0 8000 10.5 7750 13.5 7500 16.0 7250 18.0 7000 19.0 6500 22.06000 24.0 5000 24.0 4000 20.0 3000 10.0 2000 10.0 1000  8.0 0000  8.0 C.Exhaust Temperature 300-350 C. 8800  8.0 8600  8.0 8400  8.0 8200  9.08000 13.0 7750 15.0 7500 17.0 7250 19.0 7000 20.0 6500 22.0 6000 24.05000 24.0 4000 20.0 3000 10.0 2000 10.0 1000  8.0 0000  8.0 D. ExhaustTemperature 350-400 C. 8800 10.0 8600 11.0 8400 11.0 8200 12.0 8000 14.07750 15.5 7500 18.5 7250 20.0 7000 21.0 6500 22.0 6000 24.0 5000 24.04000 20.0 3000 10.0 2000 10.0 1000  8.0 0000  8.0 E. Exhaust Temperature400 C. or higher 8800 11.0 8600 11.0 8400 11.0 8200 11.5 8000 13.0 775015.0 7500 18.0 7250 19.0 7000 20.0 6500 22.0 6000 24.0 5000 24.0 400020.0 3000 10.0 2000 10.0 1000  8.0 0000  8.0

[0028] The present invention has been discussed with respect to areciprocating piston engine. The selection of different ignitionpatterns based on exhaust temperature also is applicable to other typesof internal combustion engines, such as rotary engines.

[0029] While a detailed discussion of the present invention has beenprovided above, this should be considered as illustrative and notlimiting. The present invention is not limited to the specificembodiments described herein but rather is defined by the followingclaims.

What is claimed is:
 1. A two-cycle engine, comprising: a cylinder; athrottle; a piston movable in the cylinder, for compressing a fuel-airmixture to be ignited in the cylinder, with exhaust gas from combustionof the fuel-air mixture being expelled from the cylinder; an ignitionsource in the cylinder; a controller for activating the ignition sourceat a particular point during the compressing movement of the piston, thecontroller activating the ignition source according to an ignitionpattern in which the an ignition point during the compressing movementvaries with operation speed of the engine and throttle position, theignition pattern being selected from a plurality of different ignitionpatterns; and a sensor for sensing a temperature of exhaust gas from thecylinder, the particular ignition pattern used by the controller beingselected based upon the sensed exhaust gas temperature.
 2. The engine ofclaim 1, wherein the ignition source is a spark plug and the controlleris a capacitor discharge ignition system.
 3. The engine of claim 1,wherein the sensor contacts the exhaust gas.
 4. The engine of claim 3,wherein the engine further comprises an exhaust pipe for carrying theexhaust gas and the sensor is disposed in the exhaust pipe.
 5. Theengine of claim 1, wherein individual ignition patterns are provided forexhaust gas temperature ranges that cover about 50 C.
 6. A method ofoperating a two-cycle engine, comprising: moving a piston in a cylinderto compress a fuel-air mixture in the cylinder; activating an ignitionsource in the cylinder during the compression movement; expellingexhaust gas from combustion of the fuel-air mixture from the cylinder;controlling the activation of the ignition source according to anignition pattern in which an ignition point during the compressionmovement varies with operation speed and throttle position of theengine; and sensing a temperature of the exhaust gas expelled from thecylinder; and selecting the ignition pattern from a plurality ofignition patterns based on the sensed exhaust gas temperature.
 7. Themethod of claim 6, wherein the ignition source is a spark plug and acapacitor discharge ignition system controls activation of the sparkplug.
 8. The method of claim 6, wherein the exhaust gas temperature issensed with a sensor that contacts the exhaust gas.
 9. The method ofclaim 8, wherein the engine further comprises an exhaust pipe forcarrying the exhaust gas and the sensor is disposed in the exhaust pipe.10. The method of claim 6, wherein individual ignition patterns areprovided for exhaust gas temperature ranges that cover about 50 C.
 11. Atwo-cycle engine, comprising: a cylinder; a piston movable in thecylinder, for compressing a fuel-air mixture to be ignited in thecylinder, with exhaust gas from combustion of the fuel-air mixture beingexpelled from the cylinder; an ignition source in the cylinder; acontroller for activating the ignition source at a particular pointduring the compressing movement of the piston, the controller activatingthe ignition source according to an ignition pattern in which the anignition point during the compressing movement varies with operationspeed of the engine, the ignition pattern being selected from aplurality of different basic ignition patterns; and a sensor for sensinga temperature of exhaust gas from the cylinder, the basic ignitionpattern used by the controller being modified based upon the sensedexhaust gas temperature.
 12. A two-cycle engine, comprising: a cylinder;a piston movable in the cylinder, for compressing a fuel-air mixture tobe ignited in the cylinder, with exhaust gas from combustion of thefuel-air mixture being expelled from the cylinder; an ignition source inthe cylinder; a controller for activating the ignition source at aparticular point during the compressing movement of the piston, thecontroller activating the ignition source according to an ignitionpattern in which the an ignition point during the compressing movementvaries with operation speed of the engine, the ignition pattern beingselected from a plurality of different ignition patterns; and a sensorfor sensing a temperature of exhaust gas from the cylinder, theplurality of ignition patterns including a first ignition pattern thatis selected when the sensed exhaust gas temperature is a temperaturecorrelated with an undesired operation condition.
 13. The engine ofclaim 12, wherein the temperature correlated with an undesired engineoperation condition reflects a type of fuel being used to operate theengine.
 14. The engine of claim 12, wherein the temperature correlatedwith an undesired engine operation condition reflects an engineperformance problem.
 15. The engine of claim 14, wherein the engineperformance problem is selected from the group consisting of incorrectcarburetion or incorrect fuel delivery.
 16. A method of operating atwo-cycle engine, comprising: moving a piston in a cylinder to compressa fuel-air mixture in the cylinder; activating an ignition source in thecylinder during the compression movement; expelling exhaust gas fromcombustion of the fuel-air mixture from the cylinder; controlling theactivation of the ignition source according to an ignition pattern inwhich an ignition point during the compression movement varies withoperation speed of the engine selected from a plurality of basicignition patterns; and sensing a temperature of the exhaust gas expelledfrom the cylinder; and modifying the ignition pattern selected from aplurality of ignition patterns based on the sensed exhaust gastemperature.
 17. A method of operating a two-cycle engine, comprising:moving a piston in a cylinder to compress a fuel-air mixture in thecylinder; activating an ignition source in the cylinder during thecompression movement; expelling exhaust gas from combustion of thefuel-air mixture from the cylinder; controlling the activation of theignition source according to an ignition pattern in which an ignitionpoint during the compression movement varies with operation speed of theengine; and sensing a temperature of the exhaust gas expelled from thecylinder; and selecting a first ignition pattern from a plurality ofignition patterns when the sensed exhaust gas temperature is atemperature correlated with an undesired engine operation.
 18. Themethod of claim 17, wherein the temperature correlated with an undesiredengine operation condition reflects a type of fuel being used to operatethe engine.
 19. The method of claim 17, wherein the temperaturecorrelated with an undesired engine operation condition reflects anengine performance problem.
 20. The method of claim 19, wherein theengine performance problem is selected from the group consisting ofincorrect carburetion or incorrect fuel delivery.